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In the stable version 1.5.7.10872 the FW-190 D4 has in fact an axis control option for radiator flaps, and I confirm it doesn't work. That same option also exists in 2.1.1.10527 and it has no function there either.
I guess the option was put in by mistake and we should ignore it.
Just like we ignore the axis options for TDC Slew which also appear under the FW-190's axis control options.